Rotary die apparatuses having counter-rotating die and anvil rolls are commonly used in the manufacture of cartons or boxes to trim or otherwise cut corrugated paperboard stock to a desired shape. One frequently performed trimming operation cuts away the leading edge portion of the paperboard stock. The leading edge portion is cut away by a "primary" cutting rule that extends radially outwardly from the die roll, and usually is substantially parallel to the central axis of the roll. The die roll may and frequently does also have a plurality of relatively short "trim breaker" rules that are spaced from each other along the length of the primary cutting rule and extend forwardly therefrom for the purpose of cutting the scrap leading edge portion into sections of shorter length.
The rotary die apparatus now commonly employed for cutting away the leading edge portion of the paperboard stock customarily includes at least one and usually a plurality of blocks of so-called "scrap ejection" rubber. The rubber blocks are mounted upon and extend outwardly from the curved surface of the die board of the die roll, at locations forwardly (in relation to the direction of rotation of the roll) of and closely adjacent to the primary cutting rule. In their uncompressed condition the rubber blocks project radially outwardly beyond the toothed cutting edge of the rule. The blocks are compressed as they pass into and through the nip between the die and anvil rolls. As they pass from such nip, return outward movement of the blocks is supposed to eject the cut leading edge portion of the paperboard stock downwardly away from the path of travel of the stock.
Unfortunately, however, a number of undesirable consequences may arise during use of scrap ejection means of the aforesaid conventional type. The rubber blocks may so impede the cutting action of the cutting rule as to cause pieces of the leading edge portion of the paperboard stock to remain attached to the main body of the paperboard. This is particularly likely to happen if the nip spacing between the die and anvil rolls is not properly adjusted for the particular paperboard stock being cut. The rubber blocks may alternatively or additionally drive pieces of the severed leading edge portion of the stock with such force against the urethane outer layer of the anvil roll as to cause them to adhere to the anvil roll until rotary movement of the latter carries the scrap to a position from which they are discharged onto the upper surface of the paperboard stock. In either of the aforesaid situations, the scrap paperboard may be carried with the cut paperboard product to a stacking machine downstream from the die apparatus, and may therefore eventually wind up within the carton, box or the like formed from the paperboard. This can have very undesirable consequences, particularly when the carton or box is used for foods, such as pizza, which can be contaminated by the scrap paperboard. Scrap contamination of the carton or box can also ensue when the blocks of product ejection rubber do not extend rapidly enough, as they exit from the nip between the rolls of the apparatus, to prevent the paperboard stock from advancing beneath the trimmed scrap, and then being transported by the cut paperboard stock to the packing machine.
In addition to possibly causing intermingling of the scrap material with the cut paperboard product, the use of product ejection means of the aforesaid type can cause severe structural damage to the die roll of the apparatus. This may occur when the leading edge portion of the paperboard stock engages the radially extending trailing surface of one or more of the rubber blocks with a force sufficient to displace the rubber block forwardly away from the adjacent cutting rule. Apart from possibly causing the scrap to be carried forward with the cut paperboard product, and/or causing buckling of the product's new forward end portion, the scrap material may enter into the space between the cutting rule and the forwardly deflected rubber block. As additional scrap material enters the aforesaid space during continued operation of the apparatus, the force exerted upon the cutting rule may become so great as to deflect the rule rearwardly and cause ensuing bending of the rule and/or crushing of the thereto adjacent portions of the wooden laminated die board upon which the rule is mounted. When this occurs, the apparatus must be removed from service while the damaged rule and/or die board are replaced.